1. Field of the Invention
This invention relates to digital printing. In particular, this invention relates to methods and apparatus for analyzing the characteristics of an electronic document after interpreting page description language commands that describe the document. This invention also relates to methods and apparatus for analyzing the performance of digital printing systems.
2. Description of the Related Art
Referring to FIG. 1, a conventional digital printing workflow is described. At step 10, a user creates or edits a source file using either a software application, such as a word processor, spreadsheet, presentation program, page layout tool, digital image processing program or other similar software program, or a digital device, such as a digital camera, copier, facsimile machine, scanner or other similar digital devices. A source file may include text, images, and graphics, and also may include formatting codes, font characteristics, and other similar elements. For example, a source file created in a word processing program (e.g., Microsoft® Word) may include text along with an embedded image that was created by a photo processing program (e.g., Adobe® Photoshop®), and an embedded graphic created by a spreadsheet program (e.g., Microsoft Excel). Once the source file has been created or edited, the user may want to print the document on a specific output device.
At step 12, prior to printing the source file, the user optionally may analyze the file to determine if the specific output device can print the file. Typically, the user can perform this analysis using any conventional “preflight” software program that compares the data in the source file to a set of rules, often called a “preflight profile,” associated with the specified output device. For example, a preflight profile for a particular printer may include a set of parameters listing the native fonts installed on the printer, the resolution range of the printer, and other printer parameters. If the source file includes text in a font that is not installed on the specified printer, the preflight program may report that the file may not be printed unless the font is provided to the printer as part of the print job. Similarly, if the source file includes an image that is at a resolution that is not within the printer's resolution range, the preflight program may report that the file may not be printed unless the image is converted from the specified resolution to a resolution within the printer's acceptable range. Based on the results of the preflight report, the user may return to step 10 to edit the source file, such as including a font description or modifying the resolution of an image.
Next, at step 14, the source file is translated to a page description format, such as PostScript, PDF, PCL, or any other programming language or page description language (collectively referred to herein as “PDL”) that can be recognized by an output device or processing device. A PDL file or PDL stream (collectively referred to herein as a “PDL File”) typically includes commands that describe, among other things, printer settings and print objects (e.g., pages, text, images and graphics) included in the print job. This translation step commonly occurs when a user selects a “Print” function within a source application program, which calls a printer driver that translates the source file to a PDL File. Alternatively, a user may submit the source file to some other type of software application (e.g., a distiller program), which then generates the PDL File. In either event, the printer driver or distiller program typically allows the user to specify various print options for the print job. Print options typically include many parameters that affect the appearance of the printed output, such as color mode, brightness, RGB source profile, RGB separation, CMYK source profile, output (device) profile, special black handling, spot color support, and other print options.
After the user selects the desired print options, the printer driver or distiller generates a PDL File that describes the print job. At step 16, the user optionally may analyze the PDL File using a preflight program to verify that the specified output device can print the file. Based on the results of the preflight report, the user may return to step 10 to edit the source file. Otherwise, at step 18, a raster image processor (“RIP”) interprets the commands included in the PDL File, and generates a raster description of the print job. At step 20, the specified printer receives the raster data and prints the print job.
One common problem with such previously known digital printing workflows is that final printed output may not appear as the user intended. Indeed, although preflight programs help to ensure that a digital document may be printed by a specified printer, such programs do not necessarily ensure that the digital document will be correctly printed by the printer. Thus, even though a user receives one or more clean preflight reports, the printed document nevertheless may have printing problems, such as unacceptable moiré, incorrect colors, or other printing problems. Such problems often occur because data in the source file and PDL File may be modified during the various processing steps in the digital printing workflow, sometimes without the user ever knowing that such conversions are occurring.
For example, if a user creates a source file in Microsoft Word, and imports into the document an image object that was described in a Cyan, Magenta, Yellow, Black (“CMYK”) color space, Word typically converts the image object to a Red, Green Blue (“RGB”) color space without the user knowing that such a conversion is occurring. Further, when the user generates the PDL File (e.g., via a printer driver, distiller, or other application) this conversion process may also convert color spaces of objects, add definitions that affect objects, tag objects with a name of a color space (not necessarily the correct color space), or make other changes that may affect a printed output based on the PDL File. Previously known preflight programs may not detect such changes, some of which may only affect the print job when the RIP interprets the commands in the PDL File.
In addition, a print job may print incorrectly because the user incorrectly specified print options when submitting the print job via the printer driver or distiller. Many users do not know the meaning of the various print options, and may not know how to select the options that are required to correctly print their print job. Indeed, some users may simply select default values for all print options, or may guess the values for the options. If the printed output does not print correctly, the user may modify the print options, in hopes that some combination of print options may result in a correctly printed output. Such trial and error approaches are time consuming and costly, and may be completely ineffective. Indeed, in some cases, a user may modify print options to change the appearance of an image on one page of the document, and in doing so may unwittingly change the appearance of a graphic that had been printing correctly on another page of the document. The user may give up in frustration without ever obtaining a correctly printed document.
Moreover, some printer options and factors affect only some objects in a print job, whereas other options and factors affect the entire print job. For example, a user may have specified a default output profile that is suitable for use with conventional paper stock, but may actually be printing a print job on transparency media, which requires an output profile designed for such media. Similarly, a user may have selected a halftone screen that is suitable for print jobs that include text objects, but may actually be printing a print job that consists entirely of images, for which a different halftone screen is more appropriate. In addition, if a long time has elapsed since the printer was last calibrated, a print job may print incorrectly. In general, preflight programs assume that the printer will operate in its ideal state. Preflight programs cannot check for errors in global print settings and printer factors that affect the entire print job if these factors and settings are not defined in the PDL File (e.g., a low density in one of the printer's colorants).
In view of the foregoing, it would be desirable to provide methods and apparatus to help detect problems in a print job.
It also would be desirable to provide methods and apparatus to help correct problems in a print job.
It further would be desirable to provide methods and apparatus to help specify print options for a print job.
It additionally would be desirable to provide methods and apparatus for analyzing the characteristics of an electronic document after interpreting page description language commands that describe the document.
It also would be desirable to provide methods and apparatus for analyzing global print settings and printer factors that affect an entire print job.